1. Field of Invention
The present invention relates to a converter structure for use in a receiving converter which is capable of receiving electromagnetic waves sent from a broadcast satellite or communication satellite and converting same to a first intermediate frequency signal that is output to a tuner circuit in a stage downstream therefrom, and more particularly relates to a converter structure for use in a universal LNB, universal LNBs being known as LNB converters.
2. Conventional Art
Dissemination of satellite broadcast capability to ordinary households has begun to accelerate in recent years, this representing a trend which can be observed worldwide. In accompaniment hereto, various types of receiving converters capable of being used together with antennas for receiving satellite broadcasts have been proposed, recent receiving converters—which include LNBs (Low Noise Blockdown Converters) capable of receiving frequencies over wide bands, LNBs for receiving both horizontally and vertically polarized waves, LNBs for receiving both dextrorotatorily and levorotatorily polarized waves, and so forth—exhibiting a trend toward increased number of terminals. Such general-purpose LNB converters are called “universal LNBs.”
The trend toward increased use of satellite broadcasts in various countries will now be described. Analog broadcasts via the Astra satellites (1A/1B/1C) had occupied the central role in the European market. Then, with the launching of the Astra 1D in 1994, digital broadcasts were initiated on an experimental basis in January of 1995. With the further launching of Astra 1E in October of 1995, and Astra 1F sometime around the end of 1995, a serious digital broadcast market is on its way to being established. Including both direct reception and indirect reception, receiving subscribers in Europe numbered approximately 57,000,000 homes at the end of 1994. Given such circumstances and in light of the advent of the start of digital broadcasting, increased LNB bandwidth and improved LNB stability are desired for accommodation of the two frequency bands.
Furthermore, in the U.S. market, serious digital broadcasts began around mid-1994, with subscribers increasing at a rate of one million and several hundreds of thousands of homes per month, and looking to the future it appears that several companies will be launching new digital broadcast satellites. Given such circumstances, there is also demand in the U.S. market for increased LNB bandwidth, improved LNB stability, and reduction in LNB cost. Turning to the Japanese market, digital broadcasts using JCSAT began around the spring of 1996. Moreover, digital broadcasts using Superbird began in the first half of 1997. In accompaniment to such technological trends, there is in fact ever-increasing demand for an LNB capable of receiving both digital broadcasts via CS as well as BS broadcasts.
Now, as shown in FIGS. 14 and 15, conventionally known as such a converter is a device equipped with a roughly rectangular chassis 93 to which there are secured at one side thereof (the bottom side in FIGS. 14 and 15) a terminal block 92 comprising cylindrical external conductors 90 within which central conductors are installed, and a planar block base member 91 on which a plurality of these external conductors 90 are co-mounted; a plurality of circular waveguides 94, . . . mounted so as to jut out from the other side of this chassis 93 (the top side in FIGS. 14 and 15); cap-like feedhorns 95, . . . respectively joined to the distal ends of these circular waveguides 94; rectangular waveguides 96, joined to the basal ends (located in a direction opposite feedhorns 95 from chassis 93) of the respective circular waveguides 94 and extending therefrom in a more or less perpendicular direction (in the direction of the terminal block 92), being attached thereto so as to straddle microstrip circuit boards (not shown) between themselves and prescribed locations on the circular waveguides 94; and a back cover 97 covering this chassis 93 so as to cover these rectangular waveguides 96 and the microstrip circuit boards from the back (the rectangular waveguide 96 side) thereof. Furthermore, the aforesaid circular waveguides 94, rectangular waveguides 96, chassis 93, and back cover 97 are formed from aluminum die cast alloy, the microstrip circuit boards being shielded from unwanted radiation signals and the like. Here, as shown in FIG. 16, the converter A is attached to an antenna 99 by means of an arm 98.
However, in the aforesaid conventional converter A, because the converter main body—which constitutes circular waveguides 94, rectangular waveguides 96, chassis 93, and back cover 97—is formed entirely from aluminum die cast alloy, the weight thereof is considerable. This causes the attachment procedure by which the converter A is attached to the antenna 99 to be made complicated. Moreover, considering the deformation which arm region 98 could suffer in the event of a typhoon or strong winds, arm region 98 must be reinforced with reinforcing material 89 or the like to ensure long-term reliability, this point representing a problem from the standpoint of increased materials cost.